Control device for hybrid vehicle, and hybrid vehicle incorporating control device

ABSTRACT

An ECU includes a running mode control unit, a Wout control unit, and an engine start/stop determination unit. The running mode control unit controls switching of a running mode including a CD mode in which an engine is stopped and running using a motor generator alone is given priority, and a CS mode in which the engine is operated and the SOC of a power storage device is maintained at a predetermined target. The engine start/stop determination unit carries out a start determination of the engine based on a discharge allowable power indicating electric power that can be discharged by the power storage device. The Wout control unit modifies the discharge allowable power based on the running mode and operation/stop of the engine.

TECHNICAL FIELD

The present invention relates to a control device for a vehicle, and ahybrid vehicle incorporating the control device. Particularly, thepresent invention relates to a control device for a hybrid vehicleincorporating an internal combustion engine and an electric motor as thepower source, and a hybrid vehicle incorporating the control device.

BACKGROUND ART

Hybrid vehicles are attracting attention as environment-friendlyvehicles. A hybrid vehicle incorporates a power storage device, aninverter, and an electric motor driven by the inverter, in addition to aconventional internal combustion engine, as the power source fortraction.

Japanese Patent Laying-Open No. 2009-166513 (PTL 1) discloses the methodfor suppressing overdischarge of a power storage device reliably in sucha hybrid vehicle. This hybrid vehicle is switched between an HV runningmode and an EV running mode according to the required driving forcebased on the output from various sensors. When there is a switchingrequest to the HV running during execution of the EV running mode, theengine is cranked by a motor generator receiving electric power from thepower storage device to start the engine. A discharge allowable powerWout is provided such that the voltage of the power storage device doesnot become lower than the lower limit voltage, and a torque commandvalue Tref is adjusted such that the motor consumption power does notexceed the provided discharge allowable power Wout. When the acceleratorpedal position reaches a predetermined reference value within apredetermined period of time from requesting switching to the HV runningmode, the lower limit voltage is temporarily raised.

According to this hybrid vehicle, the power storage device can reliablybe protected from overdischarge. As a result, the charging/dischargingcapability of the power storage device can be exhibited sufficiently toallow the running performance and fuel consumption performance of thevehicle to be improved (refer to PTL 1).

CITATION LIST Patent Literature PTL 1: Japanese Patent Laying-Open No.2009-166513 SUMMARY OF INVENTION Technical Problem

There is a demand for a hybrid vehicle to run in a state where theinternal combustion engine is stopped as much as possible. Recently,attention is focused on the so-called plug-in hybrid vehicle that allowsa vehicle-mounted power storage device to be charged from a power supplyexternal to the vehicle. The aforementioned demand is particularlyimmense in such plug-in hybrid vehicles.

The more the vehicle runs using only the electric motor with theinternal combustion engine stopped (hereinafter, such running is alsoreferred to as “EV (Electric Vehicle) running”, whereas running with theinternal combustion engine operated is referred to as “HV (HybridVehicle) running”), the greater heat load on electrical components. Inthis case, increasing the heat resistance of the electrical componentsmay be a possible countermeasure. However, this is not the best plansince increasing the heat resistance of electrical components may inducea great increase in cost.

In view of the foregoing, an object of the present invention is to allowEV running to be extended while giving consideration to the heat load onelectrical components in a hybrid vehicle.

Solution to Problem

According to the present invention, a control device for a hybridvehicle includes a running mode control unit, a determination unit, anda discharge allowable power control unit. The hybrid vehicle includes aninternal combustion engine generating vehicle driving force, a powerstorage device capable of being charged and discharged, and an electricmotor receiving supply of electric power from the power storage deviceto generate vehicle driving force. The running mode control unitcontrols switching of a running mode including a first mode (CD mode) inwhich the internal combustion engine is stopped and running using theelectric motor alone is given priority, and a second mode (CS mode) inwhich the internal combustion engine is operated and the state of chargeindicating a charging state of the power storage device is maintained ata predetermined target. The determination unit carries out a startdetermination of the internal combustion engine based on a dischargeallowable power (Wout) indicating the electric power that can bedischarged by the power storage device. The discharge allowable powercontrol unit modifies the discharge allowable power based on the runningmode and operation/stop of the internal combustion engine.

Preferably, when the running mode is at the first mode and the internalcombustion engine is stopped, the discharge allowable power control unitincreases the discharge allowable power than when the running mode is atthe first mode and the internal combustion engine is operating, or thanwhen the running mode is at the second mode.

Further preferably, the hybrid vehicle further includes a chargingdevice configured to receive supply of electric power from a powersupply external to the vehicle for charging the power storage device.The running mode control unit sets the running mode at the first modeafter the power storage device is charged by the charging device.

Preferably, the determination unit carries out a stop determination ofthe internal combustion engine based on the discharge allowable powerincreased by the discharge allowable power control unit when the runningmode is at the first mode and the internal combustion engine isoperating.

Preferably, the control device for a hybrid vehicle further includes arate processing unit. The rate processing unit modifies the dischargeallowable power at a predetermined rate when the discharge allowablepower is to be modified.

Preferably, the discharge allowable power control unit maintains thedischarge allowable power when the internal combustion engine is startedduring modification of the discharge allowable power.

Also preferably, the discharge allowable power control unit maintainsthe discharge allowable power when the internal combustion engine isstarted at the time of switching the running mode.

Preferably, the modifying rate of the discharge allowable power whenreturning from increase of the discharge allowable power is smaller thanthe modifying rate of the discharge allowable power when increasing thedischarge allowable power.

Preferably, the modifying rate of the discharge allowable power whenincreasing the discharge allowable power is greater than the modifyingrate of the discharge allowable power when returning from increase ofthe discharge allowable power.

Preferably, the control device for a hybrid vehicle further includes atemporary-increase processing unit. The temporary-increase processingunit temporarily increases the discharge allowable power when theinternal combustion engine is started. When the discharge allowablepower is increased by the discharge allowable power control unit, thetemporary-increase processing unit sets processing of temporarilyincreasing the discharge allowable power non-executable.

According to the present invention, the hybrid vehicle includes any ofthe control devices set forth above.

Advantageouos Effects of Invention

In the present invention, the discharge allowable power (Wout) ismodified based on the running mode and operation/stop of the internalcombustion engine. When the running mode is at the first mode (CD mode)and the internal combustion engine is stopped, the discharge allowablepower can be increased as compared to the case where the running mode isat the first mode and the internal combustion engine is operating, orthe case where the running mode is at the second mode (CS mode).Therefore, the running power during EV running can be ensured, andincrease of the heat load on electrical components can be suppressedwhen the internal combustion engine is operating and when in the secondmode. Thus, the present invention allows EV running to be extended whilegiving consideration to the heat load on electrical components.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram representing an entire configuration of ahybrid vehicle to which a control device according to an embodiment ofthe present invention is applied.

FIG. 2 is a block diagram representing a configuration of an electricsystem of the hybrid vehicle of FIG. 1.

FIG. 3 is a functional block diagram of the ECU in FIG. 2.

FIG. 4 represents the relationship between the change in SOC of thepower storage device and the running mode.

FIG. 5 represents the discharge allowable power of the power storagedevice.

FIG. 6 is a diagram to describe increase/non-increase of the dischargeallowable power according to the running mode and operation/stop of theengine.

FIG. 7 represents the discharge allowable power used in an engine stopdetermination.

FIG. 8 is a flowchart to describe a series of procedures related tocontrol of the discharge allowable power.

FIG. 9 represents the change in the discharge allowable power when theengine is to be started in a CD mode.

FIG. 10 represents the change in the discharge allowable power when theengine is to be stopped in a CD mode.

FIG. 11 represents the change in the discharge allowable power when therunning mode is switched from a CD mode to a CS mode.

FIG. 12 represents the change in the discharge allowable power when therunning mode is switched from a CS mode to a CD mode.

FIG. 13 represents the change in the discharge allowable power when theengine is to be started in association with switching the running modefrom a CD mode to a CS mode.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detailhereinafter with reference to the drawings. In the drawings, the same orcorresponding elements have the same reference characters allotted, anddescription thereof will not be repeated.

FIG. 1 is a block diagram representing an entire configuration of ahybrid vehicle to which a control device according to an embodiment ofthe present invention is applied. Referring to FIG. 1, a hybrid vehicle100 includes a power storage device 10, an ECU (Electronic Control Unit)15, a PCU (Power Control Unit) 20, a power output device 30, and adifferential gear (hereinafter, also referred to as DG) 40. Hybridvehicle 100 further includes front wheels 50L and 50R, rear wheels 60Land 60R, front seats 70L and 70R, a rear seat 80, a charging inlet 90,and a charger 92.

Power storage device 10 is a rechargeable DC power source, formed of asecondary battery such as nickel-metal hydride or lithium ion. Powerstorage device 10 is disposed at a rear side region of rear seat 80 forexample, and electrically connected with PCU 20 to supply DC voltagethereto. Power storage device 10 receives electric power generated bypower output device 30 from PCU 20 to be charged. Power storage device10 is also charged by a charger 92 connected to a charging inlet 90 andreceiving electric power supplied from a power supply external to thevehicle. Hereinafter, the power supply external to the vehicle isreferred to as “external power supply”, and the charging of powerstorage device 10 by the external power supply is referred to as“external charging”.

PCU 20 generically shows a power converter required in hybrid vehicle100. PCU 20 includes a converter boosting the voltage supplied frompower storage device 10, an inverter driving a motor generator includedin power output device 30, and the like.

ECU 15 receives various sensor outputs 17 from various types of sensorsindicating the driving state and vehicle state. Various sensor outputs17 include the accelerator pedal position corresponding to the steppingamount on an accelerator pedal 35, the vehicle speed according to therotational speed of the wheels, and the like. ECU 15 executes variouscontrol related to hybrid vehicle 100 based on such sensor outputsapplied.

Power output device 30 is provided as the driving source of the wheels,and includes motor generators MG1 and MG2 and an engine. Thesecomponents are mechanically coupled via a power split device (notshown). In accordance with the running state of hybrid vehicle 100,distribution and coupling of the driving force are implemented among theaforementioned three components via the power split device. As a result,front wheels 50L and 50R are driven. DG 40 transmits the motive poweroutput from power output device 30 to front wheels 50L and 50R, andtransmits the rotational force from front wheels 50L and 50R to poweroutput device 30. Accordingly, power output device 30 transmits themotive power from the engine and motor generator to front wheels 50L and50R via DG 40 to drive front wheels 50L and 50R. Power output device 30receives the rotational force of the motor generator by front wheels 50Land 50R to generate power and provide the generated power to PCU 20.

Motor generators MG1 and MG2 may function as a power generator and anelectric motor. Motor generator MG1 operates mainly as a powergenerator, and motor generator MG2 operates mainly as an electric motor.Specifically, motor generator MG1 receives some of the output from theengine distributed by the power split device for generating power. Motorgenerator MG1 receives supply of electric power from power storagedevice 10 to operate as an electric motor for cranking up and startingthe engine.

Motor generator MG2 is driven by at least one of the electric powerstored at power storage device 10 and the electric power generated bymotor generator MG1. The driving force of motor generator MG2 istransmitted to the driving shaft of front wheels 50L and 50R via DG 40.Accordingly, motor generator MG2 assists the engine for driving thevehicle, or for driving the vehicle by its own driving force alone. In avehicle braking mode, motor generator MG2 is driven by front wheels 50Land 50R to operate as a power generator. At this stage, the electricpower generated by motor generator MG2 charges power storage device 10via PCU 20.

PCU 20 responds to a control instruction from ECU 15 to boost the DCvoltage received from power storage device 10, and convert the boostedDC voltage into AC voltage to drive motor generators MG1 and MG2 inpower output device 30. In a regenerative operation mode of motorgenerators MG1 and MG2, PCU 20 responds to a control instruction fromECU 15 to convert the AC voltage generated by motor generators MG1 andMG2 into DC voltage for charging power storage device 10.

Charging inlet 90 is configured to allow connection with the connectorof a charging cable (not shown) connected to an external power supply.At the time of external charging, electric power is received from anexternal power supply connected to charging inlet 90. The receivedelectric power is supplied to charger 92. Charger 92 located betweencharging inlet 90 and power storage device 10 converts the electricpower supplied from the external power supply connected to charginginlet 90 to the level of the voltage of power storage device 10 foroutput thereto.

FIG. 2 is a block diagram representing a configuration of the electricsystem of hybrid vehicle 100 shown in FIG. 1. Referring to FIG. 2, theelectric system includes power storage device 10, SMRs (System MainRelay) 105 and 106, PCU 20, motor generators MG1 and MG2, ECU 15,charging inlet 90, and charger 92.

Motor generators MG1 and MG2 are connected to an engine ENG and drivingwheels not shown (front wheels 50L and 50R of FIG. 1) via the powersplit device. Hybrid vehicle 100 can run using engine ENG and motorgenerator MG2. Motor generator MG1 starts engine ENG and generateselectric power using the driving force of engine ENG.

SMR 105 is provided between power storage device 10 and PCU 20, and isset on in response to a command from ECU 15 in the event of a vehiclerunning. SMR 106 is provided between power storage device 10 and charger92, and is set on according to a command from ECU 15 in the event of anexternal charging.

PCU 20 includes a converter 110, a capacitor 120, motor drivecontrollers 131 and 132, and a converter/inverter control unit 140. Inthe present embodiment, motor generators MG1 and MG are AC motors, andmotor drive controllers 131 and 132 are formed of inverters.Hereinafter, motor drive controller 131 (132) is also referred to as“inverter 131 (132)”.

Converter 110 boosts a voltage Vm between a positive line 103 and anegative line 102 to a level greater than or equal to voltage Vb ofpower storage device 10 based on a control signal Scnv fromconverter/inverter control unit 140. Converter 110 is constituted of acurrent invertible type boost chopper circuit.

Inverters 131 and 132 are provided corresponding to motor generators MG1and MG2, respectively. Inverters 131 and 132 are connected to converter110 parallel to each other for driving motor generators MG1 and MG2based on control signals Spwm1 and Spwm2, respectively, fromconverter/inverter control unit 140.

Converter/inverter control unit 140 generates control signals Scnv,Spwm1 and Spwm2 for driving converter 110, motor generator MG1 and motorgenerator MG2, respectively, based on control command values receivedfrom ECU 15 (the target value of voltage Vm, the torque target value ofmotor generators MG1, MG2, and the like). Converter/inverter controlunit 140 outputs the generated control signals Scnv, Spwm1 and Spwm2 toconverter 110, inverter 131, and inverter 132, respectively.

According to various sensor outputs 17, ECU 15 carries out variouscontrol such as controlling the running mode of hybrid vehicle 100,engine ENG start/stop determination, charging and discharging control ofpower storage device 10, and the like. ECU 15 generates a controlcommand value to drive PCU 20, and provides the generated controlcommand value to converter/inverter control unit 140 of PCU 20. ECU 15generates and provides to charger 92 a signal for driving charger 92 inexternal charging.

FIG. 3 is a functional block diagram of ECU 15 in FIG. 2. Referring toFIG. 3, ECU 15 includes an SOC calculation unit 150, a running modecontrol unit 152, a Wout control unit 154, and an engine start/stopdetermination unit 156. ECU 15 further includes a command generationunit 158, a charge control unit 160, a rate processing unit 162, and atemporary-increase processing unit 164.

SOC calculation unit 150 calculates the SOC (state of charge) indicatingthe charging state of power storage device 10 based on voltage Vb andcurrent Ib of power storage device 10 detected by a sensor not shown.The SOC represents in 0-100% the stored amount relative to a fullycharged state of power storage device 10, and indicates the remainingstored amount in power storage device 10. For the method of calculatingthis SOC, various well-known methods can be employed.

Running mode control unit 152 controls the switching of the vehiclerunning mode based on the SOC calculated by SOC calculation unit 150.Specifically, running mode control unit 152 controls the switching to aCD (charge depleting) mode in which engine ENG is stopped and runningusing motor generator MG2 alone is given priority, or a CS (chargesustaining)mode in which engine ENG is operated and the SOC of powerstorage device 10 is maintained at a predetermined target.

Even in the CD mode, the operation of engine ENG is allowed such as whenthe accelerator pedal is stepped on greatly by the driver, when anengine driving type air conditioner is operated, when in an enginewarm-up state, or the like. The CD mode corresponds to a running mode inwhich the electric power stored in the power storage device 10 isbasically used as the energy source for running the vehicle withoutmaintaining the SOC of power storage device 10. During the CD mode, theratio of discharging is eventually relatively greater than charging. Incontrast, the CS mode is a running mode in which engine ENG is operatedas necessary and power is generated by motor generator MG1 formaintaining the SOC of power storage device 10 at a predetermined targetlevel, and is not limited to running with engine ENG always operated.

In other words, even if the running mode is at the CD mode, engine ENGwill be operated if the accelerator pedal is stepped on greatly andlarge vehicle power is required. Furthermore, even if the running modeis at the CS mode, engine ENG will stop when the SOC exceeds the targetvalue. Thus, irrespective of these running modes, running with engineENG stopped and using motor generator MG2 alone is referred to as “EVrunning”, whereas running with engine ENG operated and using motorgenerator MG2 and engine ENG is referred to as “HV running”.

FIG. 4 represents the relationship between the change in the SOC ofpower storage device 10 and the running mode. Referring to FIG. 4, it isassumed that running is started after power storage device 10 attains afully charged state (SOC=MAX) by external charging. Following externalcharging, the running mode is set at the CD mode. During running in a CDmode, the SOC generally decreases in accordance with increase of therunning distance although the SOC may temporarily be increased by theregenerative electric power generated at the time of speed reduction orthe like. When the SOC attains a threshold value Sth at time t1, therunning mode is switched to the CS mode, and the SOC is regulated at thevicinity of threshold value Sth.

Referring to FIG. 3 again, running mode control unit 152 sets therunning mode at the CD mode upon receiving a charging end signal CGENDindicating the termination of external charging from charge control unit160. Then, running mode control unit 152 outputs a mode signal MDindicating whether the running mode is at the CD mode or CS mode to Woutcontrol unit 154, engine start/stop determination unit 156, and commandgeneration unit 158.

Wout control unit 154 receives the SOC of power storage device 10 fromSOC calculation unit 150 and mode signal MD indicating the running modefrom running mode control unit 152. Wout control unit 154 receives anengine mode signal EGMD indicating whether engine ENG is operated orstopped from engine start/stop determination unit 156. Based on thesesignals, Wout control unit 154 calculates discharge allowable power Woutindicating the electric power (W) that can be discharged from powerstorage device 10.

FIG. 5 represents discharge allowable power Wout of power storage device10. Referring to FIG. 5, discharge allowable power Wout represents themaximum level of the electric power (W) that can be output from powerstorage device 10. When the SOC of power storage device 10 decreases,discharge allowable power Wout is controlled to prevent overdischarging.

In the present embodiment, discharge allowable power Wout is modifiedbased on the vehicle running mode and operation/stop of engine ENG, aswill be described afterwards. Specifically, when the running mode is atthe CD mode and engine ENG is operated, or when the running mode is atthe CS mode, discharge allowable power Wout is set at the default valueof W0. When the running mode is at the CD mode and engine ENG isstopped, discharge allowable power Wout is increased from W0 to apredetermined W1.

Charging allowable power Win is the maximum value of electric power (W)that can be input to power storage device 10. Charging allowableelectric power Win is restricted when the SOC of power storage device 10becomes high to prevent overdischarging.

Referring to FIG. 3 again, Wout control unit 154 calculates dischargeallowable power Wout (default value W0) based on the SOC of powerstorage device 10, the temperature, and the like using a map prepared inadvance. Wout control unit 154 modifies discharge allowable power Woutbased on the running mode indicated by mode signal MD received fromrunning mode control unit 152 and engine ENG operation/stop indicated byengine mode signal EGMD signal from engine start/stop determination unit156.

As shown in FIG. 6, when the running mode is at the CD mode and engineENG is stopped, Wout control unit 154 increases discharge allowablepower Wout from W0 to predetermined W1 (FIG. 5). In contrast, when therunning mode is at the CD mode and engine ENG is operated, or when therunning mode is at the CS mode, Wout control unit 154 does not increasedischarge allowable power Wout.

The reason why discharge allowable power Wout is increased when therunning mode is at the CD mode and engine ENG is stopped is to minimizethe starting frequency of engine ENG to extend EV running. In otherwords, when the accelerator pedal is stepped on and the vehicle requiredpower exceeds discharge allowable power Wout even if the running mode isat the CD mode, engine ENG is started and the vehicle is switched fromEV running to HV running to satisfy the required power.

However, the driver cannot enjoy the sense of EV running sufficiently ifengine ENG is frequently started in response to stepping on theaccelerator pedal. The present embodiment is directed to improving thesense of EV running by increasing discharge allowable power Wout tosuppress the frequency of starting engine ENG when the running mode isat the CD mode and engine ENG is stopped.

In the present embodiment, discharge allowable power Wout is not alwaysincreased. Discharge allowable power Wout is not increased when therunning mode is at the CD mode and engine ENG is operated, or when therunning mode is at the CS mode. This is to suppress increase of the heatload on electrical components (mainly converter 110), and to avoid thechange in the vehicle acceleration property between applying or notapplying the present embodiment when the engine is operated and whenrunning in the CS mode.

Referring to FIG. 3 again, Wout control unit 154 outputs to enginestart/stop determination unit 156 and command generation unit 158discharge allowable power Wout subjected to the modification set forthabove based on the running mode and engine ENG operation/stop. Further,when discharge allowable power Wout is increased, i.e. the running modeis at the CD mode and engine ENG is stopped, Wout control unit 154notifies temporary-increase processing unit 164 (described afterwards)that the discharge allowable power Wout is increased.

Engine start/stop determination unit 156 receives discharge allowablepower Wout from Wout control unit 154. Engine start /stop determinationunit 156 receives mode signal MD indicating the running mode fromrunning mode control unit 152. Engine start/stop determination unit 156carries out a start determination and stop determination of engine ENGbased on the running mode and discharge allowable power Wout.

Specifically, engine start/stop determination unit 156 calculates thevehicle required power based on an accelerator pedal position ACC,vehicle speed SPD, and the like received as various sensor outputs 17(FIG. 1). As shown in FIG. 7, when the running mode is at the CD mode,engine start/stop determination unit 156 calculates the maximum powerthat can be output from motor generator MG2 based on the increaseddischarge allowable power Wout (W1 in FIG. 5), and carries out a startdetermination and stop determination of engine ENG based on thecomparison result between the calculated maximum power and vehiclerequired power.

In other words, although the discharge allowable power Wout isnon-increased (default value W0) during operation of engine ENG when therunning mode is at the CD mode (FIG. 6), as set forth above, increaseddischarge allowable power Wout (W1) is used for the stop determinationof engine ENG. Accordingly, the stopping of engine ENG is facilitatedafter engine ENG is started in a CD mode, allowing the sense of EVrunning to be further improved.

When the running mode is at the CS mode, engine start/stop determinationunit 156 calculates the maximum power of motor generator MG2 based onthe non-increased discharge allowable power Wout (W0), and carries out astart determination and stop determination of engine ENG based on thecomparison result between the calculated maximum power and vehiclerequired power.

Referring to FIG. 3 again, command generation unit 158 generates acontrol command value for driving PCU 20 (for example, target value ofvoltage Vm, torque target value of motor generators MG1, MG2, and thelike), based on the running mode, discharge allowable power Wout, andthe engine mode indicating the operation/stop state of engine ENG.Command generation unit 158 outputs the generated control command valueto converter/inverter control unit 140 (FIG. 2) of PCU 20.

When an external power supply is connected to charging inlet 90 (FIG.2), charge control unit 160 generates and provides to charger 92 acontrol signal for driving charger 92, based on an input voltage Vac andinput current Iac detected by sensors not shown. When the SOC of powerstorage device 10 received from SOC calculation unit 150 reaches apredetermined upper limit value, charge control unit 160 ends thecharging control and outputs a charging end signal CGEND indicating theend of charging to running mode control unit 152. Accordingly, therunning mode is set at the CD mode at running mode control unit 152, asdescribed above.

Rate processing unit 162 applies rate processing to the modification ofdischarge allowable power Wout when discharge allowable power Wout isincreased from W0 to W1 and when discharge allowable power Wout returnsto W0 from W1 at Wout control unit 154. At this stage, rate processingunit 162 sets the modifying rate when discharge allowable power Woutreturns to W0 from W1 smaller than the modifying rate when dischargeallowable power Wout is increased from W0 to W1. Accordingly, theexceedance of the discharging electric power from power storage device10 over discharge allowable power Wout due to the delay in thefollowability of electric power control can be suppressed.

In other words, rate processing unit 162 sets the modifying rate whendischarge allowable power Wout is increased from W0 to W1 greater thanthe modifying rate when discharge allowable power Wout is returned to W0from W1. Thus, the hold-off state of the vehicle caused by insufficientoutput when switching from the HV running to EV running in a CD mode canbe prevented.

Temporary-increase processing unit 164 temporarily increases dischargeallowable power Wout of power storage device 10 when a great amount ofelectric power is temporarily required such as when engine ENG is to becranked up by motor generator MG1. When temporary-increase processingunit 164 has received a notification indicating that discharge allowablepower Wout is currently increased from Wout control unit 154, thetemporary-increasing processing of discharge allowable power Wout is setnon-executable. This is because the increasing processing bytemporary-increase processing unit 164 is not required since dischargeallowable power Wout is already increased by Wout control unit 154.

When engine ENG is started during modification of discharge allowablepower Wout (that is, when increasing from W0 to W1, or when returning toW0 from W1), it is desirable that discharge allowable power Wout ismaintained during startup of engine ENG at Wout control unit 154. Also,when engine ENG is started at the time of switching the running mode(when switching from a CD mode to CS mode, or from a CS mode to CDmode), it is desirable that discharge allowable power Wout is maintainedduring startup of engine ENG. By way of example, the value of dischargeallowable power Wout is maintained at the value corresponding to whenstart-up of engine ENG is initiated. Accordingly, the engine startingprocessing is stabilized since the electric power output from powerstorage device 10 at the time of starting engine ENG is stable.

FIG. 8 is a flowchart to describe a series of procedures related tocontrol of discharge allowable power Wout. Referring to FIG. 8, ECU 15uses a map or the like prepared in advance to calculate dischargeallowable power Wout (default value W0) (step S10).

Then ECU 15 determines whether the running mode is at the CD mode, andengine ENG is stopped (step S20). When a determination is made that therunning mode is not at the CD mode (i.e. in a CS mode), or when engineENG is operating (NO at step S20), ECU 15 proceeds to the processing ofstep S70 that will be described afterwards.

When a determination is made that the running mode is at the CD mode andengine ENG is stopped at step S20 (YES at step S20), ECU 15 increasesdischarge allowable power Wout from W0 to a predetermined W1, as shownin FIG. 5 (step S30).

When discharge allowable power Wout is to be modified, ECU 15 executesrate limit processing in which the modifying rate of discharge allowablepower Wout is limited (step S40). Further, ECU 15 determines whether astarting request of engine ENG is made during modification of dischargeallowable power Wout (step S50). When a determination is made thatstarting of engine ENG is required during modification of dischargeallowable power Wout (YES at step S50), ECU 15 maintains dischargeallowable power Wout (step S60). By way of example, discharge allowablepower Wout is maintained at a value corresponding to when start-up ofengine ENG is requested.

Then, ECU 15 carries out Wout restriction processing (step S70). By wayof example, discharge allowable power Wout is limited when the SOC ofpower storage device 10 becomes low, as shown in FIG. 5. Alternatively,discharge allowable power Wout may be limited when the temperature ofconverter 110 rises or the like.

Then, ECU 15 determines whether starting of engine ENG is requested ornot (step S80). When a determination is made that starting of engine ENGis requested (YES at step S80), ECU 15 further determines whetherdischarge allowable power Wout is currently increased or not (step S90).When a determination is made that discharge allowable power Wout is notcurrently increased (YES at step S90), ECU 15 executes thetemporary-increasing processing of discharge allowable power Wout (stepS100).

In other words, when a determination is made that discharge allowablepower Wout is currently increased at step S90 (YES at step S90), adetermination is made that temporary-increasing processing is notrequired since discharge allowable power Wout is already increased.Therefore, control proceeds to step S110 without executing step S100.

The change in discharge allowable power Wout according to various changein situation is shown in FIGS. 9-11.

FIG. 9 represents the change in discharge allowable power Wout when theengine is to be started in a CD mode. Referring to FIG. 9, “EV” of theengine mode refers to EV running with engine ENG stopped. “CRK” refersto receiving supply of electric power from power storage device 10 forengine ENG to be cranked by motor generator MG1. “HV” refers to HVrunning with engine ENG operated.

Prior to time t1, engine ENG is stopped (engine mode “EV”), anddischarge allowable power Wout is increased to W1. Increase value W1 isalso used for the engine start/stop power threshold value.

When the vehicle required power exceeds the engine start/stop powerthreshold value at time t1 in response to the accelerator pedal beingpushed down or the like, engine ENG is cranked up (engine mode “CRK”).Since discharge allowable power Wout is already increased to W1, thetemporary-increasing processing of discharge allowable power Wout inassociation with cranking of engine ENG is not executed.

When engine ENG is started at time t2 (engine mode “HV”), dischargeallowable power Wout returns to W0 from W1. At this stage, the modifyingrate of discharge allowable power Wout is limited to prevent thedischarging power from exceeding discharge allowable power Wout due to asudden reduction of discharge allowable power Wout.

The engine start/stop power threshold value is still at the increasedvalue of W1, as set forth above, even if engine ENG is started. Thisfacilitates the stopping of engine ENG after engine ENG has beenstarted.

FIG. 10 represents the change in discharge allowable power Wout when theengine is stopped in a CD mode. Referring to FIG. 10, prior to time t3,engine ENG is operated (engine mode “HV”), and discharge allowable powerWout is at W0 (non-increase). As mentioned above, increased value W1 isemployed for the engine start/stop power threshold value.

When the vehicle required power becomes lower than engine start/stoppower threshold value (W1) at time t3, a stop processing of engine ENGis executed (engine mode “STP”). Accordingly, discharge allowable powerWout is increased from W0 to W1. Although the modifying rate ofdischarge allowable power Wout is limited when increased from W0 to W1,likewise the return to W0 from W1, the modifying rate at the time ofincreasing from W0 to W1 is greater than the modifying rate whenreturning to W0 from W1 to prevent a hold-off state of the vehiclecaused by insufficient power.

FIG. 11 represents the change in discharge allowable power Wout when therunning mode is switched from a CD mode to CS mode. Referring to FIG.11, prior to time t11, it is assumed that the running mode is at the CDmode and engine ENG is stopped (EV running). Therefore, dischargeallowable power Wout is increased to W1, and the increased value of W1is employed for the engine start/stop power threshold value.

When the SOC of power storage device 10 reaches a threshold value Sth attime t11, the running mode is switched to the CS mode (FIG. 4).Accordingly, discharge allowable power Wout returns to W0 from W1.Similarly at this stage, the modifying rate of discharge allowable powerWout is limited to prevent exceedance of the discharging power overdischarge allowable power Wout caused by a sudden reduction of dischargeallowable power Wout.

In contrast to the CD mode in which the engine start/stop powerthreshold value is still at the increased value of W1 (FIG. 9) even whenengine ENG was started, the engine start/stop power threshold value isswitched to W0 here since the running mode is switched to the CS mode.

FIG. 12 represents the change in discharge allowable power Wout when therunning mode is switched from a CS mode to CD mode. Referring to FIG.12, the running mode is at the CS mode prior to time t12. Therefore,discharge allowable power Wout is W0 (non-increase), and W0 is used forthe engine start/stop power threshold value.

When the running mode is switched to the CD mode at time t12, dischargeallowable power Wout is increased from W0 to W1. It is assumed thatengine ENG is stopped. Although the modifying rate of dischargeallowable power Wout is limited at this stage, the modifying ratethereof is greater than when the running mode is switched from a CD modeto CS mode (FIG. 11) since discharge allowable power Wout is increased.The switching of the running mode to the CD mode causes the enginestart/stop power threshold value to be switched to W1.

FIG. 13 represents the change in discharge allowable power Wout whenengine ENG is started in association with switching the running modefrom a CD mode to CS mode. Referring to FIG. 13, it is assumed that therunning mode is at the CD mode and engine ENG is stopped prior to timet21 (engine mode “EV”). Therefore, discharge allowable power Wout isincreased to W1.

At time t22, the SOC of power storage device 10 reaches threshold valueSth, and the running mode is switched to the CS mode (FIG. 4).Accordingly, discharge allowable power Wout begins to return to W0 fromW1 according to a predetermined modifying rate.

At time t22 during modification of discharge allowable power Wout,starting of engine ENG is requested, and engine ENG is cranked up(engine mode “CRK”). Accordingly, discharge allowable power Wout ismaintained at the value corresponding to that of the point of time t22,during engine mode “CRK”. When engine ENG is started and cranking ofengine ENG ends at time t23 (engine mode “HV”), discharge allowablepower Wout begins to change towards W0.

In the case where discharge allowable power Wout is lower than the valuesubsequent to Wout-increase by temporary-increase processing unit 164(FIG. 3) at the point of time t22 when the cranking of engine ENG isstarted, discharge allowable power Wout may be maintained at the valuesubsequent to Wout-increase by temporary-increase processing unit 164(FIG. 3).

In the present embodiment, discharge allowable power Wout is modifiedbased on the running mode and operation/stop of engine ENG, as set forthabove. Accordingly, when the running mode is at the CD mode and engineENG is stopped, discharge allowable power Wout can be increased thanwhen the running mode is at the CD mode and engine ENG is operating, orthan when the running mode is at the CS mode. Therefore, the runningpower during EV running can be ensured, and increase of heat load onelectrical components during operation of engine ENG and during a CSmode can be suppressed. According to the present embodiment, EV runningcan be extended while giving consideration to the heat load onelectrical components.

In the present embodiment, a charging inlet 90 and charger 92 forexternal charging are provided. The running mode is set at the CD modeafter external charging. Therefore, the present embodiment allows EVrunning using electric power by external charging to be extended.

Since a stop determination of engine ENG is carried out based onincreased discharge allowable power Wout (W1) when the running mode isat the CD mode and engine ENG is operating in the present embodiment,the stopping of engine ENG is facilitated after engine ENG has beenstarted in a CD mode. Therefore, the sense in EV running can be furtherimproved by the present embodiment.

Moreover, since discharge allowable power Wout is maintained when engineENG is to be started during modification of discharge allowable powerWout or at the time of switching the running mode in the presentembodiment, the electric power output from power storage device 10 atthe startup of engine ENG is stable. Therefore, the engine startingprocessing is stabilized in the present embodiment.

Moreover, the modifying rate when discharge allowable power Wout returnsto W0 from W1 is set smaller than the modifying rate when dischargeallowable power Wout is increased from W0 to W1 in the presentembodiment. Therefore, the exceedance of the discharging electric powerfrom power storage device 10 over discharge allowable power Wout causedby the delay in the followability of electric power control can besuppressed.

In other words, the modifying rate when discharge allowable power Woutis increased from W0 to W1 is set greater than the modifying rate whendischarge allowable power Wout returns to W0 from W1 in the presentembodiment. Therefore, the hold-off state of the vehicle caused byinsufficient output when switching from the HV running to EV running ina CD mode can be prevented in the present embodiment.

When discharge allowable power Wout is currently increased by Woutcontrol unit 154 in the present embodiment, the temporary-increasingprocessing of discharge allowable power Wout by temporary-increaseprocessing unit 164 is set non-executable. Accordingly, dischargeallowable power Wout can be prevented from being increased unnecessarilyin the present embodiment.

The above embodiment has been described based on a configuration inwhich only one power storage device 10 and one converter 110 areprovided. However, the present invention is also applicable to anelectric system in which a plurality of power storage devices andconverters are provided (for example, an electric system including aplurality of power storage devices, and a plurality of convertersconnected parallel thereto).

Furthermore, although the embodiment has been described in whichexternal charging is carried out with an external power supply connectedto charging inlet 90, external charging may be carried out by anon-contact feeding method such as by resonance, electromagneticinduction, and the like.

In the foregoing, engine ENG corresponds to an example of “internalcombustion engine” of the present embodiment. Motor generator MG2corresponds to an example of “electric motor” of the present invention.Engine start/stop determination unit 156 corresponds to an example of“determination unit” of the present invention. Wout control unit 154corresponds to an example of “discharge allowable power control unit” ofthe present invention. Furthermore, charging inlet 90 and charger 92constitute an example of “charging device” of the present invention.

It should be understood that the embodiments disclosed herein areillustrative and nonrestrictive in every respect. The scope of thepresent invention is defined by the terms of the claims, rather than thedescription of embodiment set forth above, and is intended to includeany modification within the scope and meaning equivalent to the terms ofthe claims.

REFERENCE SIGNS LIST

10 power storage device; 15 ECU; 17 various sensor outputs; 20 PCU; 30power output device; 35 accelerator pedal; 40 DG; 50L, 5OR front wheel;60L, 60R rear wheel; 70L, 70R front seat; 80 rear seat; 90 charginginlet; 92 charger; 100 hybrid vehicle; 105, 106 SMR; 110 converter; 120capacitor; 131, 132 inverter; 140 converter/inverter control unit; 150SOC calculation unit; 152 running mode control unit; 154 Wout controlunit; 156 engine start/stop determination unit; 158 command generationunit; 160 charge control unit; 162 rate processing unit; 164temporary-increase processing unit; MG1, MG2 motor generator; ENGengine.

1.-11. (canceled)
 12. A control device for a hybrid vehicle, said hybridvehicle including an internal combustion engine generating vehicledriving force, a power storage device capable of being charged anddischarged, and an electric motor receiving supply of electric powerfrom said power storage device for generating vehicle driving force,said control device controlling switching of a running mode including afirst mode in which said internal combustion engine is not operated tomaintain a state of charge indicating a charging state of said powerstorage device, and a second mode in which said internal combustionengine is operated or stopped, and said internal combustion engine isoperated to maintain said state of charge, and said control devicesetting a startup power larger, when said running mode is at said firstmode, than when said running mode is at said second mode, said startuppower indicating a vehicle required power that causes said internalcombustion engine to be started when said hybrid vehicle is runningusing said electric motor with said internal combustion engine stopped.13. The control device for a hybrid vehicle according to claim 12,wherein said control device sets a stop power larger, when said runningmode is at said first mode, than when said running mode is at saidsecond mode, said stop power indicating a vehicle required power thatcauses said internal combustion engine to be stopped when said hybridvehicle is running with said internal combustion engine operated. 14.The control device for a hybrid vehicle according to claim 13, whereinsaid stop power when said running mode is at said first mode is equal tosaid startup power when said running mode is at said first mode.
 15. Thecontrol device for a hybrid vehicle according to claim 12, said hybridvehicle further including a charging device configured to receive supplyof electric power from a power supply external to the vehicle to chargesaid power storage device, wherein said control device sets said runningmode at said first mode after said power storage device is charged bysaid charging device.
 16. A control device for a hybrid vehicle, saidhybrid vehicle including an internal combustion engine generatingvehicle driving force, a power storage device capable of being chargedand discharged, and an electric motor receiving supply of electric powerfrom said power storage device for generating vehicle driving force,said control device setting a running mode at a first mode in which thehybrid vehicle runs without maintaining a state of charge indicating acharging state of said power storage device until said state of chargeis reduced to a predetermined threshold value, and switching saidrunning mode to a second mode in which the hybrid vehicle runs with saidstate of charge maintained when said state of charge reaches saidpredetermined threshold value, and said control device setting a startuppower larger, when said running mode is at said first mode, than whensaid running mode is at said second mode, said startup power indicatinga vehicle required power that causes said internal combustion engine tobe started when said hybrid vehicle is running using said electric motorwith said internal combustion engine stopped.
 17. A control device for ahybrid vehicle, said hybrid vehicle including an internal combustionengine generating vehicle driving force, a power storage device capableof being charged and discharged, and an electric motor receiving supplyof electric power from said power storage device for generating vehicledriving force, said control device controlling switching of a runningmode including a first mode in which the hybrid vehicle runs with atleast said electric motor as a driving force source and a state ofcharge indicating a charging state of said power storage device becominglower in accordance with increase of a running distance, and a secondmode in which said internal combustion engine is operated or stopped,the hybrid vehicle runs with at least one of said internal combustionengine and said electric motor as the driving force source, and saidstate of charge is maintained, and said control device setting a startuppower larger, when said running mode is at said first mode, than whensaid running mode is at said second mode, said startup power indicatinga vehicle required power that causes said internal combustion engine tobe started when said hybrid vehicle is running using said electric motorwith said internal combustion engine stopped.
 18. A control device for ahybrid vehicle, said hybrid vehicle including an internal combustionengine generating vehicle driving force, a power storage device capableof being charged and discharged, and an electric motor receiving supplyof electric power from said power storage device for generating vehicledriving force, said control device comprising: a running mode controlunit controlling switching of a running mode including a first mode inwhich said internal combustion engine is not operated to maintain astate of charge indicating a charging state of said power storagedevice, and a second mode in which said internal combustion engine isoperated or stopped, and said internal combustion engine is operated tomaintain said state of charge, and a discharge allowable power controlunit increasing, when said running mode is at said first mode and saidinternal combustion engine is stopped, a discharge allowable power thatcan be discharged by said power storage device than when the runningmode is at said first mode and said internal combustion engine isoperating, or than when said running mode is at said second mode. 19.The control device for a hybrid vehicle according to claim 18, furthercomprising a determination unit carrying out a start determination ofsaid internal combustion engine based on said discharge allowable power.20. The control device for a hybrid vehicle according to claim 19,wherein said determination unit carries out a stop determination of saidinternal combustion engine based on discharge allowable power increasedby said discharge allowable power control unit, when said running modeis at said first mode and said internal combustion engine is operating.21. The control device for a hybrid vehicle according to claim 18, saidhybrid vehicle further including a charging device configured, toreceive supply of electric power from a power supply external to thevehicle for charging said power storage device, wherein said runningmode control unit sets said running mode at said first mode after saidpower storage device is charged by said power storage device.
 22. Thecontrol device for a hybrid vehicle according to claim 18, furthercomprising a rate processing unit modifying said discharge allowablepower at a predetermined rate in modification of said dischargeallowable power.
 23. The control device for a hybrid vehicle accordingto claim 22, wherein said discharge allowable power control unitmaintains said discharge allowable power when said internal combustionengine is started during modification of said discharge allowable power.24. The control device for a hybrid vehicle according to claim 22,wherein said discharge allowable power control unit maintains saiddischarge allowable power when said internal combustion engine isstarted at a time of switching said running mode.
 25. The control devicefor a hybrid vehicle according to claim 22, wherein a modifying rate ofsaid discharge allowable power when said discharge allowable powerreturns from an increased state is smaller than the modifying rate ofsaid discharge allowable power when said discharge allowable power isincreased.
 26. The control device for a hybrid vehicle according toclaim 22, wherein a modifying rate of said discharge allowable powerwhen said discharge allowable power is increased is greater than themodifying rate of said discharge allowable power when said dischargeallowable power returns from an increased state.
 27. The control devicefor a hybrid vehicle according to claim 18, further comprising atemporary-increase processing unit temporarily increasing said dischargeallowable power when said internal combustion engine is started, whereinsaid temporary-increase processing unit sets processing of temporarilyincreasing said discharge allowable power non-executable when saiddischarge allowable power has been increased by said discharge allowablepower control unit.
 28. A control device for a hybrid vehicle, saidhybrid vehicle including an internal combustion engine generatingvehicle driving force, a power storage device capable of being chargedand discharged, and an electric motor receiving supply of electric powerfrom said power storage device for generating vehicle driving force,said control device comprising: a running mode control unit setting arunning mode at a first mode in which the hybrid vehicle runs withoutmaintaining a state of charge indicating a charging state of said powerstorage device until said state of charge is reduced to a predeterminedthreshold value, and switching said running mode to a second mode inwhich the hybrid vehicle runs with said state of charge maintained whensaid state of charge reaches said predetermined threshold value, and adischarge allowable power control unit increasing, when said runningmode is at said first mode and said internal combustion engine isstopped, a discharge allowable power that can be discharged by saidpower storage device than when said running mode is at said first modeand said internal combustion engine is operating, or than when saidrunning mode is at said second mode.
 29. A control device for a hybridvehicle, said hybrid vehicle including an internal combustion enginegenerating vehicle driving force, a power storage device capable ofbeing charged and discharged, and an electric motor receiving supply ofelectric power from said power storage device for generating vehicledriving force, said control device comprising: a running mode controlunit controlling switching of a running mode including a first mode inwhich the hybrid vehicle runs with at least said electric motor as adriving force source and a state of charge indicating a charging stateof said power storage device becoming lower in accordance with increaseof a running distance, and a second mode in which said internalcombustion engine is operated or stopped, the hybrid vehicle runs withat least one of said internal combustion engine and said electric motoras the driving force source, and said state of charge is maintained, anda discharge allowable power control unit increasing, when said runningmode is at said first mode and said internal combustion engine isstopped, a discharge allowable power that can be discharged by saidpower storage device than when the running mode is at said first modeand said internal combustion engine is operating, or than when saidrunning mode is at said second mode.
 30. A hybrid vehicle comprising acontrol device defined in claim
 12. 31. A hybrid vehicle comprising acontrol device defined in claim 18.